Apparatus for testing the running of timepieces



Aug. 11, 1936. R. TAMM 2,050,866

APPARATUS FOR TESTING THE RUNNING OF TIMEPIECES Filed Feb. 19, 1954 iMaia/Hong 4Z Mofo/VONK Il g4 g5 Patented Aug. Il, 1936 imitan STATSAPPARATUS FOR TESTING THE RUNNING OF TIMEPIECES Application February 19,1934, Serial No. 212,002 In Germany February 25, 1933 The simplestmethod of testing watches, clocks or other timepieces consists incomparing the distance travelled by the hand of the clock, at the end ofa sufficient length of time, with the indication of a standard clock. Assoon as special accuracy is required from a clock, however, such amethod of testing is ,extremely inconvenient, because perceptibledifferences between the clock under test and the standard clock ariseonly after a number of hours. tain a high degree of accuracy, a numberof corrections are necessary in most cases, approximately a week must betaken for the regulation sf a. timepiece to secure accurate running.

In order to avoid this delay, it has already been proposed to test therunning of clocks by comparing the frequency determined by theoscillations of the balance of the clock under test with a standardfrequency, which is preferably produced, for instance, by an accuratelyrunning clock with the same transmission or gear'ratio betweenescapement wheel and hand as the clock under test. mine differences inthe shortest possible time, it has furthermore been proposed to effectthis frequency comparison by exciting the stator of a small single-phasesynchronous motor with one frequency and the rotor of the motor with theother frequency, so` that the rotor shifts in accordance with the phasedisplacement between the two frequencies. 'I'his shift may be read oi atan indicator.

According to the present invention, the accuracy of the testing methodlast-mentioned can be further improved and the energy expenditurenecessary for the indication can bereduced if the phase displacementbetween the frequencies under comparison is rendered visible at acurrent indicating or current-responsive instrument, which is suppliedfrom a current source with current impulses, the duration of whichcorresponds to the phase difference existing at the time between the twofrequencies. To this end, use is made preferably of two relays, one ofwhich is energized, for instance, in step with the frequency of theclock under test, while the other is energized in step with the standardfr equency. The two relays are so coupled together that'they act on'oneanother in such a. manner that, on the switching-in of one, the other iscie-energized. If the instrument is connected in a circuit controlled byone relay. then the duration of the current impulses flowing throughthis instrument is dependent upon the phase displacement between the twofrequencies. Any

Since, in order to ob- In order to be able to deterchange in thedeflection of the instrument thus indicates a phase displacement and itis possible to decide without difficulty, from the direction o f thechange in deflection, whether the clock under test is running fast orslow, if it is made clear from which of the two frequencies the relayswitching the instrument circuit is being energized.

There are the following suitable possibilities of forming a frequencyfrom the movement of the balance of a clock. The-individual beats of theanchor or the escapement wheel may be allowed to act through amicrophone on an amplifier. This particularly simple methodv isdiscussed in detail below.`

In the accompanying drawing, Fig; 1 is a diagrammatic representation ofone form of my invention; Fig. la is a diagram illustrating certainrelations of voltage and current in the operation invention isillustrated in principle. Any suitable means may be employed forproducing frequencies corresponding respectively to the running of astandard time piece and of the time piece under test. As an example, Ihave indicatedat 3l the watch or other time piece to be tested, and at32 a standard watch of the same type as the watch to be tested, that isto say a standard watch having the same normal number of beats perminute. Both watches are placed (on any suitable support or holder)adjacent to two microphones 4l and 42 respectively, of any ordinary orapproved construction, so that the beat noises of the watches will acton said microphones. 'Ihe microphones are connected in circuit (in awellknown manner) with amplifiers 5l and 52 respectively, in order tointensify the relatively weak fluctuations of voltage produced in themicrophones, so that the intensied fluctuations will be strong enough toactuate devices having the character of relays. In the exampleillustrated by Fig. 1, the amplified voltages of one frequency, forinstance, the frequency of ,the watch 3| under test, are applied to thegrid of an ionic controlling tube I and the voltage impulses of thestandard frequency derived from the watch 32 through .the parts 42, 52are applied to the grid of an ionic controlling tube 2.

'I'hese controlling tubes, a's is well-known, have the property thatthey can easily be started by an auxiliary voltage, but that extinctionis possible only by breaking the anode: circuit.v 3 is a condenser, 4 acurrent indicating apparatus,- 5 and 6 are resistances, 'I is alimitrelay and l any well-known circuit or source forobtaining a constantvoltage. 'Ihe indicating. instrument 4, to which only current impulsesare supplied, should be damped suiliciently in order to obtain a steadypositionof the pointer, scriber, or other indicating element. For thispurpose, I may emf.

ploy any well-known or approved expedients.

'I'he mode of operation of the arrangement will beclear from Fig. 1a. Inthis figure, Ia denotes those voltage peaks which are applied to thegrid of the ionic controlling tube I in accordance with the frequencyunder test. By 2a are denoted the voltage peaks which are applied to thegridl of the ionic controlling grid 2 in accordance with the standardfrequency. Below the illustration of the time interval of these voltagepeaks, I have indicated the time interval during which the current Jflows through the instrument l. The rectangles showny in Fig. larepresentthe current impulses flowing through said instrument, theheight of each rectangle is determined by the constant voltage and theresistances in the circuit and is therefore constant, while the width ofeach rectangle corresponds to the time interval between the voltagepeaks Ia and 2a. In other words, in the lower portion of Fig. la theordinates represent current, and the abscissa time, in correspondence tothe time intervals represented by the absciss at the upper portion ofFig. la. As soon as the first impulse has started the tube I, a currentows through this tube, the

instrument 4, the resistance 5 and the limit relay 1 The limit relay 1does not respond because it is so dimensioned that it requires the sumof the anode currents of both tubesin order to respond. As soon as thetube 2 is lighted or startedI sistance of such tube was comparativelylow,

while at the same time the internal resistance of the tube 2 waspractically with points of dierent potenals, and consequently thecondenser was 'in the charged condipensated or balanced fully by thedischarge curftion. At the moment that the tube 2` is lighted or startedas above 'referred to, the condenser 3 will be discharged'in impulsefashion through both tubes I and 2. The discharge current of thecondenser will increase thel anode current nowing through the tube 2,but will decrease the anode current lflowing through the tube I. If thecondenser 3 is of proper size, the anode current in the tube I willatthat moment be comrent of the condenser, so that the tube I; will beextinguished. The instrument circuit is thus temporarily devoid ofcurrent and is switched on again only by the next voltage peak Ia, whichstarts the tube I and, through` the condenser 3, extinguishes the tube2. The pointer of the instrument is thus adjusted to a mean value, whichtely great. 'Ihe .Y -two condenser plates therefore were connected isdependent upon the ratio ofthe length of time during which current isflowing through the in strument 4, to the length of time during whichthe instrument is devoid of current. By selecting a sufficiently dampedinstrument, a stationary position of the pointer is thus obtained, whichonly varies when a frequency displacement takes place between the twoseries of impulses.

Under the above assumption that the tube'I isV being controlled by thefrequency of the watch under test, an increasing .deflection of theinstrument l indicates -that the voltage peaks 2a are increasinglylagging behind the voltage peaks Ia and that, therefore, the frequencyof the watch under test is higher than the standard frequency. On theother hand, a decrease in the deflection of the pointer would indicatethat the watch under test is running slow.

The use of ionic controlling tubes as` relays has the advantage that thetime constant of the relaywis practically zero and thus need not beconsidered at all, and that, above all, there is voltage peaks Ia and2a. momentarily overlap on phase displacement. If both tubes are started*i simultaneously, the condenser V3 thenremains inactive and currentwould flow continuously through both-tubes. This'double anode currentcauses the limit relay 1 to respond. This momenthe individual comparison1 prevent the measur'eadvantage muy opens trie anode circuit of bethtubesfso that nowthe arrangement ls-again readyA to operate. Y

It is proposed above to derive the frequency ofthe time piece under testand, in certain circumstances, also the frequency of the standard timepiece, electrically bymeans of the periodi-1 cally moving parts of thetime piece,for instance. the balance, the anchor, the escapement wheelor the like, by a microphone influenced by the percussive noises of thetime piece. It has been found that. in this case, vdifficulties arestill to be overcome because, in the electro-acoustic reception ofnoises, no precisely marked and regu' larly recurring individual voltagepeaksA are ob-.-

tained, which may be used without diiliculty, I

after suitable amplification, for operating the relay. 'I'.he ticking ofthetime piece, which has avery marked sound effect on the ear, as can beseen from the illustration of an oscillograph 'record in Fig. 2,produces a whole group of voltage N peaks which greatly vary in height,and the rhythm and height of which vary considerably within thedifferentl periods. To this extent the precise time control of a relayoffers Aconsiderable diiilculties, quite apart from the fact that acertain noise intensity exists during the whole time period, even duringietime when no noise can be detected by theear, so that. therefore, thesensitivity of the arrangement receiving the sound and controlling therelay cannot -be determines to any desired degree. since the above mencned group. of voltage peaks, moreover, occupies acomparatively largeproportion of each period, .the further difficulty arises that the twofrequencies interfere. with one another, this being the case when thephases of the two frequencies are almost equal.v In this case it mayhappen that the first voltage peak of the time piece which is slightlyleading energizes the relay and reverses the armature and that directlyafterwards the first voltage peak of the slightly lagging frequency setsthe relay to the other position and then, however, a further voltagepeak of the leading frequency wrongly re-establishes the initialposition and thus falsifies the indicated result. A

In order to obviate the above described diiculties, another feature ofmy invention makes special provisions to determine clearly the beginningand end of the impulses within the periods. An important means for-this, according to the invention, consists in locking theimpulse-controlled relay arrangement immediately after its excitationagainst an excitation which takes place in the same sense, this lockingbeing effected for a length of time which must be less than a fullperiod. By this means, above all, the relay armature is prevented, ashas been briefly mentioned above, from being reversed again in anundesirable manner by the relay being operated too long.

A further step in this direction consists in using a special amplifyingarrangement for coupling the time pieces producing the frequencies andthe relay arrangement, the amplifier being purposely constructed in sucha manner that the amplification departs as far as possible fromlinearity. If this deviation takes place in such a manner that thedegree of amplification greatly increases withincreasing controllingvoltage, then substantially only the higher voltage peaks are amplifiedand the lower voltage peaks are rendered practically completelyineffective. If,'on the contrary, the amplifier is so dimensioned thatit operates near a maximum value, then the higher voltage peaks areamplified only up to about the same degree as the lower peaks, so thatthen a more uniform operation is also the result'.

As is clear from the mode of operation of the arrangement illustrated inFigure 1, it is important that the duration of the impulses shouldcorrespond as accurately as possible to the phase difference between thetwo frequencies. To this end, however, it is necessary that points ofthe period which are as sharply defined as possible should be used forforming the impulses. In general, the above mentioned measures satisfythe conditions to be fulfilled. However, there are time pieces withwhich sufficiently accurate test results are diflicult to obtain bythese means alone, because the noise threshold of these clocks,- thatis, the minimum value of `the alternating voltage caused by theirconstant noises A is, at the outset, unfavourably high and, in addition,the peaks produced by the beats of the anchor or escapement wheel areparticularly irregular or else a so-called preliminary beat" is producedby the actual beat. In these cases it may be preferable, instead of theabove described measures, to integrate the voltage peaks over the entireperiod by rectifying them or cutting ofi' a half and thus obtaining awave current which is caused to act on the relay arrangement. This wavecurrent still contains any i'rregularities which result" from4V thedifferences between the individual periods. Thus, in many cases, therewould be no object in using it directly for controlling the measuringcircuit.

A constructional example of the invention is diagrammaticallyillustrated in Fig. 3. Reference numerals l0 and denote two coils, for

instance, two telephone coils which are energized in accordance with therunning noises produced by the watch 3| under test and by a standardwatch 32. At Illa an Ha, I have indicated the diaphragms of therespective telephones. Reference numerals |2 and I3 denote twoamplifiers having a rectifier and electrical oscillatory circuit, theoscillatory circuits being tuned to the standard frequency and undamped.The output coils It and i5 energize by the oscillatory circuits act ontwo coils I6 and l'l, which are provided in the grid circuits of twoionic relays i9 and i9. Reference numeral 20 denotes the common gridbias battery and 2| and 22 are two condensers which, on starting of theanode current of the respective tube, are so charged through transformer23 and 26 and rectiers 25 and 26 that the further part of the voltagecurve proceeding from the coils I6 can no longer` cause the ioniccontrollers to respond. 'I'he condensers 2| and 22 discharge in thecourse of a period through the rectiers 25, 26 and the secondary coilsof the transformers 23 and 24. Should the resistance of the rectifers inthe blocking direction be too great, then special discharge resistancesmay also be provided for the condensers.

The reference numeral 2l denotes the common anode battery of the twotubes, 9 the instrument which is connected in the anode circuit of onetube and 29 a condenser. by means of which the tubes extinguish oneanother. The reference numeral 30 denotes a limit relay, which respondsif both ionic controllers should happen to have been simultaneouslystarted.

The operation should be quite clear. If, for instance, the ionic tube |8is lightedor started rst, its grid is lockedf for approximately thedu-ration of a period. At the same time, the instrument 9 is traversedby a current, the strength of which is constant if the voltage of thecurrent source 21 is constant. As soon as the tube I9 is started, itcauses the tube I8 to be extinguished due to the discharging impulse ofthe condenser 29. Consequently, the instrument ilv v becomes devoid ofcurrent until the tube I8 is again started. In this manner, therefore,the running of the time piece under test can easily be read from thechange in the deflection of the measuring instrument 9. v

Instead of the ionic controllers, in certain circumstances, mechanicalrelays may be used. An example of a simple construction of this type isshown in Fig. 4. The parts 4, 8, 3|, 32, tl, 42, 5|, and 52 correspondto those designated by the 'same reference characters as in Fig. 1.Direct current supplied by the source or device 8 serves to energize arelay having two coils 6| and 62 adapted to exert opposite attractionson an armature 63, constructed with a tendency not to remain in acentral position, but to rest either against a contact 64 or against astop 65. When the coil 6| is energized by an impulse resulting from aheat noise in the watch 3| under test. the armature 63 will be attractedto engage the contact 66, thereby closing the circuit of the instrument6. This circuit remains vclosed until an impulse resulting from a beatnoise of the standard watch 32 energizes the coil 62, thus bringing thearmature 63 to the right-hand position, against the stop 65, and openingthe circuit of the instrument t. The instrument circuit will remain openuntil the next beat noise of the watch under test again energizes thecoil 6|. The indications of the instrument t will tal-re place exactlyas explained with reference to Fig. la, that is to say, if the watchunder test is running at the correct speed, the time inter.- vals duringwhich the instrument 4 receives current will be equal, and theindication of the instrument constant (if proper damping of theinstrument is employed, as stated above). If the watch under test isrunning slow, the time intervals during which the instrument l receivescurrent will decrease progressively, and the indications of suchinstrument will show a corresponding progressive decrease. Similarly,

if the watch under test is fast (gaining on the standard watch), thetime intervals during which the instrument 4 receives current willincrease progressively, with a corresponding increase in the deflectionor indication of such instrument. I prefer to use a highly dampedindicating instrument, -and the pointer which is indicated by the arrowin Figs. 1, 3, and 4 may be considered as connected with a coil mountedto turn about the axis of the pointer, this being a well known typeofelectrical indicating instrument.

I claim:

1. In a device for testing the running of time ,Y

pieces, a highly damped current indicating instrument, a current source,means for producing in connection with a time piece a series ofelectrical impulses in accordance with the rhythm of the periodicallymoving parts of the time piece under test, means for producing a secondseries of electrical impulses, of a standard frequency which,corresponds to that which the rst mentioned sries of impulses exhibitson the correct e riodically moving parts of the time piece under 55.4disconnecting said instrument from the source by 75 '4. In a device iortesting the runningv of test, means for producing a second sries ofelectrical impulses, of a standard frequency which corresponds to thatwhich the ilrst mentioned series of impulses exhibits on the' correctrunning of the clock under test, and means for connecting the saidinstrument to the current source by each' impulse of one series ofimpulses and each impulse of the other series of impulses.

3. In a device for testing the running o! time pieces, a highly dampedcurrent indicating instrument, a current source, means for producing inconnection with a time piece a series of electrical impulses Ainaccordance withthe rhythm of the periodicallymoving parts of the timepiece `under test, means for producing a second series of electricalimpulses, the frequency of which corresponds to thatwhich the iirst4mentioned series of impulses exhibits on the correct running of thetimepiece under test, and a-relay on which the `impulses of both series ofimpulses act in suchamanner that the said instrument is connected to thecurrent source by each impulse of one series of impulses and isdisconnected from the current source byeach impulse of the other `seriesof impulses.A

pieces, a highly damped current indicating injstrument, a currentsource, means Ior producing in connection with a time piece a series ofelectrical impulses in accordance with the rhythm of the periodicallymoving parts of the time piece under test, means for producing a secondseries of electrical impulses, the frequency of which corresponds tothat which the iirst mentioned series of impulses exhibits on thecorrect running of the time piece under test, ampliers for saidimpulses, two ionic controlling tubes, each of which can be started byone series of impulses through said ampliers, means operatedby thestarting of one ionic controlling tube to cause the other to beextinguished, and connections by which the current indicating instrumentis 1ocated in the anode circuitof one of the two tubes. A'

5. In a device for testing the running of time pieces, a highlydamped'current indicating instrument, a source of current, means forproducing in connection with a time piece a series of electricalVimpulses in accordance with the rhythmof the periodically moving partsof the time piece under test, means for producing asecond series ofelectrical impulses, the frequency of which corresponds to that whichthe iirst mentioned series of impulses exhibits on the correct runningof the time piece under test, ampliers for said impulses, two ioniccontrol tubes,

tion and so dimensioned that, on starting of the anode current of onetube, the other tube is extinguished, and means by which the currentindicating instrument is inserted in the anode circuit of one tube.

6. In a device for testing the runningof time pieces, a highly dampedcurrent indicating instrument, a source of current, means for produc-Ving in connection with a time piece a series of electrical impulses inaccordance with Athe rhythm of the periodically moving parts of the timepiece under test, means for producing a second series of electrical impes, the frequency of which corresponds to that which the rst mentionedseriesof impulses exhibit on .the correct running oi' the time pieceunder test, am

plii'lers for said impulses, two ionic vcontrol tubes, each of which canbey started by a series of im-- pulses through said ampliers, meanswhich,- on the ignition of one ionic control tube, cause the other to beextinguished, the currentindicating instrument being connected in the`anode circuit of one of the two tubes, a limit relay which is insertedin an anode circuit common to both tubes and soadiusted that it iscaused to re- V'spond by the sum of the anode currents of the two tubes,and a contact opening on operation of; said limit relayv and arranged inthe anode circuit of one of said ionic control tubes.

'1. In a' device for-testing the running of timepieces, a highly 'dampedcurrent indicating instrument, a source of current, a microphone forpicking up the periodic running noises of the time piece under test, anamplifier the input side of which is connected with said microphone toproduce a. series of impulses corresponding to the rhythm of saidnoises, means for producing a series of electrical impulses of astandard frequency which corresponds vto that frequency which therunning noises of the time piece under test will exhibit onoorrectfrunning, means for'75 providing, in spite of unavoidableirregularities in the runing noises, a series of impulses with equalintervals, a relay to which the output of the ampliiier is so connectedand on which the impulses 0f the rst mentioned series of electricalimpulses act in such a manner that the indicating instrument isconnected to the current source by each impulse of one of said series ofimpulses and is disconnected from the current source by each impulse ofthe other of said series of impulses.

8. In a device for testing the running of time pieces, a highly dampedcurrent indicating instrument, a current source, a microphone forpicking up the periodic running noises of the time piece under test, anamplifier, a connection from the microphone to the input stage of theamplifying arrangement, to produce a series of impulses corresponding tothe rhythm of said noises, means for producing a series of electricalimpulses, the frequency (standard frequency) of which corresponds tothat which the running noises of the time piece under test will exhibiton correct running, a relay to which the output of the amplifier is soconnected and on which the impulses of the series of electrical impulsesof standard frequency act in such a manner that the indicatinginstrument is connected to t-he current source by each impulse of one ofsaid series of impulses and that the said instrument is disconnectedfrom the current source by each impulse of the other of said series ofimpulses, and means for locking the relay immediately on or after theaction of an impulse, against further impulse connections of the sameseries of impulses for a time which is less than the interval betweentwo impulses of the same series of impulses.

9. In a device for testing the running of time pieces, a highly dampedcurrent indicating instrument, a current source, means for producing aseries of electrical impulses in accordance with the rhythm ofperiodically moving parts of the time piece under test, means forproducing a second series of electrical impulses of a standard frequencywhich corresponds to that which the first mentioned series of impulsesexhibits on the correct running of the time piece under test, amplifersfor said impulses, two ionic control tubes. each of which is ignited bya series 'of impulses through said ampliers, means which, by theignition of one of the ionic control tubes, cause theY other to beextinguished, the current indicating instrument being connected in theanode circuit of one of the two tubes, and condensers which are soconnected in series with the control grids of the said tubes and to theanode circuits of the said tubes that, on starting of the anode current,the condensers are charged whereby the control grids are temporarilyrendered insensitive to' further controlling impulses.

10. In a device for testing the running of time pieces, a highly dampedcurrent indicating instrument, a current source, a microphone forpicking up the periodic running noises of the time piece under test, anamplifier the input stage of which is connected with said microphone toproduce a series of impulses corresponding to the rhythm of said noises,means for producing a series of electrical impulses, the frequency`(standard frequency) of which corresponds to that which the runningnoises of the .time piece under test will exhibit on correct running, arelay arrangement to which the output of the amplifier is so connectedand on which the impulses of the series of. electrical impulses ofstandard frequency act in such a manner that the indicating instrumentis connected to the current source by each impulse of ore of said seriesof impulses and the indicating instrument is disconnected from thecurrent source by each impulse of the other of said series of impulses,the amplifier connected between the microphone and the relay being soconstructed that the amplification curve will exhibit a considerabledeparture from linearity.

11; In a device for testing the running of time pieces, a highly dampedcurrent indicating instrument, a current source, a microphone forpicking up the periodic running noises of the time piece under test, anamplifier to the input stage of which the microphone is connected, toproduce a series of impulses corresponding to the rhythm of said noises,means for producing a series of electrical impulses, the frequency(standard frequency) of which corresponds to that which the runningnoises of the time piece under test exhibit on correct running, a relayto which the output of the amplifier is so connected and on which theseries of electrical impulses of standard frequency act in such a mannerthat the indicating instrument is connected to the current source byeach impulse of one of said series of impulses and the indicatinginstrument is disconnected from the current source by each impulse ofthe other of said series of impulses, g'qrectier to which the irregularvoltage peaks proceeding from the microphone are supplied` in such amanner that a wave current of the frequency of the periodically movingparts 'of the time piece underA test is formed, an oscillatory structurewhich is tuned to the standard lfrequency and excited by this Wavecurrent, .said oscillatory structure being connected to `tide relay insuch a manner that the relay is causiry to respond at certain points ofthe substantially sinusoidal Voltage variations arising in the1roscillatory structure.

12. In a' system for testing the running of time pieces by comparisonwith a standard, means for producing in connection with a time pieceunder test, a series of electrical impulses in accordance with therhythm of the periodically moving parts of such time piece, means forproducing a second series of electrical impulses of a standard frequencywhich corresponds to that which the first mentioned series of impulseswill exhibit on the correctrunning of the time piece under test, anindicating circuit having connections to receive said impulses, and

means whereby said indicating circuit will be rendered operative by eachimpulse of one of said series of impulses and inoperative by eachimpulse of the other series.

13. In a system for testing the running of time pieces by comparisonwith a standard, means for producing in connection with a time pieceunder test, a series of electrical impulses in accordance with therhythym of the periodically moving parts o such time piece, means forproducing a second series of electrical impulses of a standard frequencywhich corresponds to that which the first mentioned series of impulseswill exhibit on the correct running of the time piece under test, anindicating circuit including a source of current and an indicatinginstrument, and means for connecting said instrument to the currentsource by each impulse of one of saidseries of impulses anddisconnecting said instrument from said source by each impulse of theother series.

14. In a. system for testing the running of.

CII

means whereby said indicating circuit will be renderedV operative byeach impulse of one of said series of impulses-and inoperative by eachimpulse of the other series,

15. In a system for testing the running ofv time piecesby comparisonwith a standard. a plurality of microphones for picking up the periodicsounds of a/standard'time piece and of the time piece under test, andthus producing two series of electrical impulses, anindicating circuitincluding a source of current and an indicating instrument, and meansfor connecting said instrument to the current source by each impulse ofone of said series of impulses and disconnecting said instrument fromsaid source by each impune 'of the other series.

16. In a device for testing the running oi.'

time -pieces, a highly' damped current indicating rect running of thetime piece under test. amplitiers for said impulses, two ionic controltubes. each of which can be started by a series of im. pulses throughsaid ampliiiers, means which,"on the ignition of one ionic control tube,cause the other to be extinguished,'the current indicating instrumentbeing connected in the anode circuit of one of the two tubes, a limitrelay which is inserted in an anode circuit common to both tubes and soadjusted that it is caused to respond by the sum of the anode currentsof the two tubes, and a contact opening on operation zu of said limitrelay and arranged in the anode circuit of both of said ionic controltubes.

RUDOLF Tama,

vmentioned series of impulses exhibit on the cor-

